Tonga Tsunami at Marsden Point 

Data kindly supplied by Mulgor Consulting Ltd. and Silver Fern Shipping Ltd.

Commentary

Marsden Point is strongly affected by far infra gravity ( FIG ) waves, which are modulated with the tide, being higher at high tide. However, FIG waves tend to have periods of 6 to 20 min, so the very long waves in mid-morning of 4 May, may be the first tsunami waves. The large waves at high tide could be a superposition of FIG and tsunami waves. Marsden Point is in direct line with Tonga, so for the sites under consideration, the tsunami would be expected to reach here first.

Figure 1. Tonga tsunami at Marsden Point showing: A. long wave record; B. significant (red) and maximum (blue) wave heights, and high tide times (green diamonds); C. period of significant waves; and D. distribution of significant wave height with time and period. EQ denotes the time of the earthquake. Times are in NZST (UTC + 12).

How were these calculated?
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